Étape 2 - Evaluate a site and size the ram pump
First of all, it is necessary to find surface water that continuously flows on a sufficiently steep slope (about 10% minimum). If it's a dam or lake, make sure that there are positions below.
To evaluate a site, 4 parameters have to be estimated (as shown on the scheme) :
- q water flow
- H lift height
- L driving line lenght
- h fall height
Concerning the water flow, it it not necessary to be really precise, an average value would be enough to size the system. Several techniques are available, depending on your material and time : see Water flow estimation"
The water flow can vary a lot depending on the seasons, so it could be relevant to establish a maximal and minimum flow throughout the year.
The lift height corresponds to the height difference between the pump height and the water reservoir. Concretely you should decide where you want the water to arrive, and measure the height difference between this point and the water source (in average). This measure will be precised later in the process. Slope measuring can be done with this website https://www.geoportail.gouv.fr/carte :
Place GPS coordinates on the map, and use the function "asymetric profile". This correspond to a curve showing the elevation depending on the distance (in m).
The driving line lenght and the fall height are directly related to the river or lake slope. In this case as well, it would be interesting to establish an asymetric profile in order to take distances and elevation gradients into account.
Once the parameters of the site are identified, we will size the pump in order to retrieve the needed flow and a minimal installation coast (the smaller the pump is, the cheaper it will be).
Determine L, H and h:
General Formula: q=((h*Q)/(h + H))0.70
Where 0.70 is the pump efficiency and Q the arrival flow.
Concretely, you will need:
You can also use a fall diagram as shown on the picture to determine H and h.
Sizing of the pump:
To size the pump itself, you have to chose the needed arrival flow. One of the easiest ways to do that is to use the provided table, that gives the final pipe size according to the source flow, the elevation ratio h/H and the final flow.
Using the table, you can proceed as follows:
- Choose the final flow, corresponding to you water needs
- Find the corresponding number in the table according to the elevation ratios of your site
- Do not hesitate to oversize the system in case of doubt
- Verify that you water flow is higher than indicated in the table
- On the same table line, you can read the relevant pump sizing for you situation
You obtain the battery pipe (or driving line) diameter D, which is the same for all other components of the pump.
For example: 26x34 to an internal diamter of 26mm and an external diameter of 34mm
Be careful because the dimensions given are in milimeters but can sometimes be indicated in inches.
| Millimeters (mm)
| Inches
|
| 15x21
| 1/2
|
| 20x27
| 3/4
|
| 26x34
| 1
|
| 33x42
| 1 1/4
|
| 40x49
| 1 1/2
|
| 50x60
| 2
|
All pump components will therefore be of the same dimension, except for the outlet pipe (or delivery pipe) whose diameter D' will be half of the driving line D. D'=D/2
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